The diploma thesis deals with the issue of determining fire accelerators in samples after extinguishing. The aim of the work is to determine the residues of the fire accelerator in samples of different kinds of materials after combustion, under different conditions (burning time, extinguishing time, the presence of the accelerator). Also assessing the possibility of application of an absorbent material (cotton wool, pulp) to capture accelerators from a given sample when they are soaked in extinguishing water. The samples were examined by the method of connection of headspace system, gas chromatograph, mass spectrometer (HS-GC-MS). Natural and synthetic materials were used in the individual experiments - lignocellulosic material (straw), polyurethane (PUR) foam, and insulating (EPS) expanded polystyrene. Natural-95 gasoline was used to accelerate the fire of some samples. Most volatile compounds were found in samples from PUR foam burning with using an accelerator, the minimum amount of compounds was identified in the case of EPS combustion without the use of gasoline. The main products identified were substances of alkanes, alkenes, aromatic hydrocarbons, benzene derivatives and etc. By comparing different sampling methods, it was found that the most effective method in the case of burning EPS and PUR appears to be the collection of extinguishing water. The analysis showed that the effectiveness of cosmetic cotton wool is highest in the experiments of burning of straw and EPS using gasoline as an accelerator. The obtained results show that the method of sampling by absorption on cellulose wadding appears to be the least effective for all samples, with and without gasoline. The correct determination of flame retardants can help in the final stage to confirm the intentional nature of the fire or, conversely, to refute the intentional intent.